netdev - Re: using software TSO on non-TSO capable netdevices

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Date:	Thu, 31 Jul 2008 04:36:52 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, akarkare@...vell.com,
	nico@....org
Subject: Re: using software TSO on non-TSO capable netdevices

On Thu, Jul 31, 2008 at 10:29:24AM +0800, Herbert Xu wrote:

> > Index: linux-2.6.27-rc1/net/ipv4/tcp_output.c
> > ===================================================================
> > --- linux-2.6.27-rc1.orig/net/ipv4/tcp_output.c
> > +++ linux-2.6.27-rc1/net/ipv4/tcp_output.c
> > @@ -1544,7 +1544,7 @@ static int tcp_write_xmit(struct sock *s
> >                        break;
> > 
> >                if (tso_segs == 1) {
> > -                       if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
> > +                       if (unlikely(!tcp_nagle_test(tp, skb, 5 * mss_now,
> >                                                     (tcp_skb_is_last(sk, skb) ?
> >                                                      nonagle : TCP_NAGLE_PUSH))))
> >                                break;
> 
> What's the size of your application's write calls?

The maximum that splice will allow -- PIPE_BUFFERS * PAGE_SIZE.

I.e. the writes should be large enough.
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